An important thing to understand when playing Starcraft. When playing as a Zerg, every building and colony you create expands a circle of "living, moving dirt" called the creep. Zergs can only build upon the creep, and it transfers all the resoursces, so your minerals get transported. You can only build a Nydus canal gateway from one creep area to another.

In urban parlance, to creep is to cheat on one's significant other while attempting to conceal said activity. A person may be said to be "on the creep" if they look to consistently creep. To be caught creeping is an excellent way to end up a) dead, b) single, or c) married, with c) usually being caused by an ultimatum brought about by the discovery of the illicit affair by the aforementioned significant other.

Creep in materials is a slow continuos process where the material slowly deforms over time.
To creep the material has to be under load - temperature only accelerates the process. Creep will occur under any load - the stress does not have to be over the yield strength of the material.

A common example of creep is light bulbs - when lit, the tungsten filament heats up to around 2000 degrees C. While this is way below the melting point of tungsten (above 3000 deg C), it is hot enough to initiate creeping in the material. At this temperature it will slowly bend downwards under the force of gravity, and permanently elongate. When it reaches it's maximum elongation, it breaks off - and the light goes out.

The critical temperature when creep starts is typically 30-40% of the melting temperature.
Therefore, ice creeps rapidly even at very cold temperatures (-30 C) this is because -30 C is really 88% of the melting temperature of ice. At room temperature we also see that lead is at 50% of melting temperature, which explains why lead pipes deform with age.

There are two main consequences of creep:

At constant load, the material deforms over time. This is typical with glaciers, turbines, and structures. The material is subject to the same load (most often plain old gravity), and therefore will bend permanentely - given enough time.

At constant displacement, the load will decrease. Bolts and other pre-tensioned fasteners are often affected by this. The bolts doesn't go anywhere, but they get longer - and therefore relaxes. Bolts on engine blocks needs tightening from time to time. A funny thing here is that the more you tighten the bolt, the quicker it will creep, and the faster it will need re-tightening....

Final fracture occurs when the creep has elongated the defects inside the material so much that the rest material cannot handle the load. This is why most turbine blades are made out of a single grain. A single grain structure minimizes the defects inside the material, and it becomes much less suceptible to creep fracture.

To avoid creep you need to select materials with a high melting point. As stated, the working temperature needs to be under 30% of the melting temperature. If this cannot be avoided, one should alloy the material to make it less creepy (the technical term is to maximise obstructions to dislocation motion...).

A Zerg colony relies entirely upon the creep. The only structure that can live independently is the hatchery. Zerg drones can build a hatchery on bare ground because the Hatchery itself is a creep colony. There are only two types of creep colonies - hatcheries and smaller creep colonies; smaller creep colonies still require creep to be contructed, however.

The way a creep colony works is simple. Inside the colony it produces spores in the liquidchemical it stores. It pumps the spores up through a tube and as they travel it fertilizes them. They then reach the "mouth" of the colony and it expels the spores into the air. They then settle on the ground nearby, and begin to germinate. Once they start to grow a purple biological layer covers the ground like a skin. It roots itself into the ground and absorbs the nutrients from it. As the creep grows the creep colonies expel their spores further and further away, until they have expelled them to the maximumdistance possible, then they repeat the process from close by again. If a creep colony is destroyed and it cannot supply spores to the creep, the creep will die and recede.

Constructs built on the Creep root themselves into it and not the ground. This is because they require nutrients, however can only use one type. The creep works by converting the nutrients found on any planet into the same nutrients found on Char (see Zerg), so that no matter where the Zerg are they can still spread. Originally the Zerg did not rely on this Creep, however once the Zerg started to spread and structures could not survive on the foreign planets, the Overmind created this creep.

As the creep is biological, it is soft and spungy and unstable. As such, foundations cannot be laid and any Terran or Protoss contructs would simply collapse if built upon the creep. Hence, the Terran and Protoss cannot build constructs on creep. This limits the Terran and Protoss in Zerg land, however it is a double edged sword, as the Zerg cannot build without it, hence will find it difficult to impede on Protoss and Terran ground.

Reply to Mr100percent: Not all buildings spread the creep, only hatcheries and creep colonies.